The present invention relates to a tunnel excavator for forming an upper half annular hollow space in the solid earth.
It has been commonly developed to use explosives in excavating a tunnel in the rocks or the solid earth. However, when explosives are used, public obstructions such as explosion sounds and vibrations thereby will take place and, depending upon the circumstances, such construction work as using explosives sometimes must be given up.
On the other hand, machines for mechanically excavating entire cross-section of a tunnel has been developed. However, the machines for excavating the entire cross-section of a tunnel of a large size are fairly expensive and, depending upon the scale of the construction work, such expensive machines can not be adopted.
In order to avoid such an expensive machine, there has been developed a process for forming a tunnel wherein an upper half annular hollow space is first formed by excavating the earth in accordance with the tunnel excavation plan and the support structure is applied to the outer boundary of the thus formed upper half annular hollow space so that the excavation is advanced to about 15m. Then, the remaining earth within the upper half annular hollow space is crushed by using explosives and removed to form the entire cross-section of the tunnel. This process is useful in that the vibration caused by the explosion of the explosives is prevented from directly propagating to the surface of the ground thereby giving a solution to the prevention of the public obstruction.